Stabilizers on chips AMS1117xx. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Stabilizers on chips AMS1117xx. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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Chips of the AMS1117, LD1117A, IL1117A series (analogous to K1254ENxx, Transistor Plant, Minsk) are linear voltage regulators of positive polarity with low saturation voltage, produced in SOT-223 and ID-Pack packages. Available for fixed voltages of 1,2, 1,5, 1,8, 2,5, 2,85, 3,3, 5,0 volts and 1,25 V adjustable.

The output current of microcircuits is up to 1 A, the maximum power dissipation is 0,8 W for microcircuits in the SOT-223 package and 1,5 W in the D-Pack package. The microcircuits have a built-in protection system for temperature and power dissipation. The built-in overheat protection system reduces the output voltage and current, preventing the crystal temperature from rising above 150°C. The thermal protection system does not replace a heat sink.

It can be a strip of copper foil of a printed circuit board, a small copper, brass plate, heat-conducting ceramics. The microcircuit is attached to the heat sink by soldering a heat-conducting flange or glued to the body and flange using heat-conducting glue. The use of microcircuits of these series provides increased stability of the output voltage (up to 1%), low current and voltage instability coefficients (less than 10 mV), higher efficiency, which makes it possible to reduce the input supply voltages. Chips of the 1117 series are widely used in computer technology: as part of motherboard circuits, video, sound cards, TV tuners, various controllers.

On fig. 1 shows a diagram of a power supply - a positive polarity voltage stabilizer for a fixed output voltage of 3,3 V. The input voltage of the stabilizer can be in the range of 4,6 ... 12 V.

This stabilizer is ideal for powering various mobile pocket devices with self-powered 3 V. It can be used as a miniature power supply or used as a plug-in stabilizer for mains adapters - traditional transformers and modern switching ones, for example, used to charge cell phones. This stabilizer can also be connected to the vehicle's +12 V electrical system via an LC noise filter. Diode VD2 is designed to protect the stabilizer from incorrect connection. Inductor L1 and capacitors C1-C3 are designed to suppress network interference.

If you need a more powerful stabilizer, then its circuit needs to be a little more complicated by adding one transistor VT1 and resistor R1 to it, fig. 2.

Stabilizers on chips AMS1117хх

The KT818 series transistor in a plastic case can dissipate up to 1 W of power, in a metal case up to 2,5 ... 3 W. If more power is required, then the transistor should be installed on a heat sink. That would be the best solution. if both the transistor and the microcircuit are installed on a common heat sink, one case is as close as possible to the other. Since, with such a switching scheme, the protection of the microcircuit against overcurrent will not work, so as not to significantly complicate the circuit of the device, it is possible to power the stabilizer through a self-restoring fuse.

If a transistor in a plastic case is used, for example, KT818A, then the maximum load current can be up to 8 A, if in a metal one, for example, KT818BM, then 12 A. If you want to build your own version of the stabilizer on a 1117 series chip, you can use the data from Table. 1.

Stabilizers on microcircuits ams1117-xx

The pinout of the microcircuit is shown in fig. 1. The heat sink flange is connected to the output of the chip. If it is necessary to increase the output voltage of the stabilizer, for example, by 0,3 ... 0.7 V, then an appropriate low-power silicon diode, for example KD521A, can be installed in the power circuit break and the common output of the microcircuit, with an anode to the microcircuit, shunted with an oxide capacitor of 47 μF 3,3, 10...XNUMX V.

Stabilizers on chips AMS1117хх

At the same time, the instability of the output voltage of the microcircuit will increase markedly, but still remain quite acceptable for most applications.

Author: Butov A.L.

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